Maybe Critism is too strong a word to use.
The word we've all been using is critique, not criticism. There's a difference.A small one, but important one. One implies negativity (criticism) and one implies being critical (critique). There's nothing wrong with being critical. What is terrible is telling people whether you like it, or dislike it, and not saying why. Then your opinions are useless.
When I see someone is trying to learn, I will other an opinion about options which may or may not help the poster, mainly about moving around the scene to bet better angles, compostion and exlude things.
So that's critique then
That's fine, but how could another beginner know if their work is being critiqued by another beginner? I think it's important that they can make that distinction. After all, another beginner may just take your opinion at face value and act upon it, and let's be honest.... if you're a beginner yourself how confident are you about your own advice?
This is why opinions are useless in crit. You're entitled to an opinion on the work, and your entitled to give that opinion, but someone less confident, or a beginner themselves will not be able to separate the meaningful advice from the crap.
There's a prevailing opinion in here that all advice is equally valid. Where's thins idea coming from? It only seems to be internet forums that think like this, particularly this one. Would you accept medical advice from anyone? Financial advice? No... you'd check the credentials of the person giving that advice, or at least assume someone else has on your behalf. I've seen people arrive on here as beginners, and within a week they're giving crit left right and centre. Now.. before you all jump down my throat, I don't think that's a BAD thing either, because learning to give useful crit is actually a great way to learn yourself. All some of us are saying, is that the more experienced among us can spot the armchair pundits a mile off, but not everyone else can, so it would be great to see the work of those giving critique on our own work. After all, if you're receiving crit from someone who's work is clearly rubbish, we can chose to ignore it, or at least pick out the useful bits from the rubbish.
Some advice, such as exposure, and technical things can be given by anyone with a bit of technical knowledge, sure, but that's often the least useful crit. The subjective stuff like composition, content etc, then that requires a good working knowledge of the genre you're critiquing. After all, if your sum total of knowledge of from Practical Photography and your local camera club, then that's gonna show in your work, and if I can see your work, I can then make a judgement on how you think photographically, and therefore whether your opinion on it is relevant or not.
My advice still stands: Look at someone's work before accepting their crit at face value. They may be rubbish - or at least never produce any work of the type you do, and therefore almost certainly have no experience in that genre.
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If you receive technical crit on lighting, or processing, then how good is that person's lighting or processing? If you're receiving crit on a fashion shoot, then how good is that person's fashion work? If you receive crit on portrait work, how good is their portrait work? etc etc. If I received crit on my photoshop editing for example, and the person critting my work is clearly crap at it themselves, then surely their advice is probably crap too.